The sound of rolling thunder, an extended noise that seems to move, is a result of the fact that sound travels relatively slowly.
Thunder comes from air exploding in the intense heat of lightning. A lightning bolt may travel as far as 2 miles (3 kilometers) at a rate of about 93,000 miles (148,800 kilometers) per second.
At ground level, sound travels about a mile (1.6 kilometers) in 5 seconds. So what we hear as a roll of thunder is simply the delayed noise of the lightning traveling. It sounds as if it is traveling because it is.
It has been said that it would take 200 million trumpeters blasting for 13 seconds to reproduce the amount of noise in one peal of thunder.